[AVX-512] Use 512-bit vcvtps2ph/vcvtph2ps to implement fp_to_f16/f16_to_fp when F16C and VLX are not supported.

Fixes PR23941.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@281958 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed